Optical sighting devices such as riflescopes are often used to aid the aiming of weapons, such as rifles, pistols, bows, or the like. Such optical sighting devices typically include reticles, which may take various forms, such as cross-hairs, posts, circles, horseshoes, a dot, or other suitable shapes, to help a shooter aim at the target. In addition to riflescopes, reticles are also sometimes included in binoculars, spotting scopes and other optical sighting devices, particularly such devices used by a spotter of a spotter-shooter team to assist a shooter in aiming a weapon using a separate riflescope. Some reticles include various marks, such as optical range finding marks to facilitate estimating a distance to a target of known size, holdover aiming marks for adjusting for the ballistic drop of a projectile for targets located at various ranges from the shooter, and various other marks to assist the shooter in acquiring information, or adjusting for variables relating to weapon inclination, crosswinds, or other shooting conditions.
In a typical arrangement, a riflescope includes an objective that forms an inverted image of a distant target at a front focal plane behind the objective, and an image-erecting lens or prism assembly located between the front focal plane and an eyepiece of the riflescope. The erecting lens assembly or prism assembly erects the inverted image of the target to form an erect image at a rear focal plane viewable through the eyepiece in a field of view thereof. In a variable-power riflescope, lens elements of the erector assembly are movable along their optical axis to change a magnification of the image at the rear focal plane. The riflescope may include a reticle at either the front focal plane, the rear focal plane, or both.
When the reticle is located at the front focal plane (FFP reticle), its apparent size viewed through the eyepiece is affected by adjustments to the optical magnification to the same degree as the image of the distant target. In essence, the apparent size of both the image and the FFP reticle will be scaled with changes in magnification so that a user will perceive that the reticle covers (that is, overlies or obstructs) the same portion of the distant target regardless of changes in the optical magnification.
On the other hand, a riflescope with a reticle positioned at the rear focal plane (RFP reticle) has different characteristics. In particular, since the reticle is displayed at the rear focal plane behind the erector assembly, any changes in magnification or focus typically do not affect the apparent size of the RFP reticle as viewed through the eyepiece. Accordingly, when the user increases the image magnification by moving elements of the erector assembly, the apparent size of the target will be enlarged, but the apparent size of the RFP reticle in the field of view will remain unchanged. The RFP reticle will simply be superposed on the magnified erect image at the rear focal plane and the user will see the same reticle size regardless of the magnification. In such cases, the user will perceive that the RFP reticle covers (that is, overlies or obstructs) different amounts or portions of the distant target as the amount of optical magnification changes.
In some instances, it may be desirable to include the reticle in the front focal plane so that the reticle scales in size with the target so as to not disorient the shooter. In other instances, it may be desirable to include the reticle in the rear focal plane so that the apparent size of the reticle is not changed when the image is magnified.
The present inventors have identified a need for an improved optical sighting device that combines selected features of an FFP reticle and an RFP reticle to provide enhanced features and/or flexibility for a user.